a) Field of the Invention
This invention relates to a manhole or catch basin assembly and more especially a manhole or catch basin assembly comprising separable component parts which assemble to a unitary structure, still further the invention relates to a frame as a principal component of such manhole or catch basin assembly, to an assembly of a lower structure and a manhole or catch basin assembly and to a method of inhibiting transmission of mechanical vibrations through a manhole or catch basin assembly to a lower structure.
b) Description of Prior Art
Manholes which provide access to sewers or utility components and catch basins for removal of rainwater, typically employ a lower support structure, for example, a concrete riser in which access steps may be mounted, a frame assembly typically of metal above the lower structure and a removable cover typically of metal to close and permit access to the lower structure and a conduit network communicating with the concrete riser.
A manhole typically has access steps to facilitate entry into the hole.
An adjustment riser is disposed between the lower structure, for example, a concrete riser and the frame assembly. The adjustment riser has two functions, first it occupies the gap between the lower structure and the frame assembly to complete the assembly of the manhole or catch basin hole, and secondly it absorbs mechanical vibrations developed above the frame assembly, such as by vehicles travelling over the metal cover when the hole is located in a road, and inhibits transmission of the mechanical vibrations to the lower structure, which mechanical vibrations would otherwise cause fractures or cracking in a concrete riser as the lower structure, shortening its life such that frequent repair or replacement becomes necessary.
In that the adjustment riser is to occupy a gap formed in part as a result of a lack of exactness in dimensions of components of the manhole or catch basin; and in part as a result of variations in requirements of different hole structures, such adjustment risers are fabricated in a variety of different thicknesses to accommodate different gap heights between the lower structure and the frame assembly in different holes. An adjustment riser of required thickness or a combination of thicknesses is then selected based on measured dimensions of the gap at a particular hole structure.
The component parts of a manhole or catch basin assembly are typically manufactured at poor manufacturing precision, such that a cover or closure member which is the uppermost component located generally flush with an exposed paved surface such as a road surface, fits poorly in the manhole or catch basin assembly and may bounce or vibrate as vehicles travel over it. The other components of the assembly also poorly fit and gaps exist which provide a path for flow of water throughout the assembly structure.
Furthermore, the frame, which is the principal component of the manhole or catch basin assembly is typically of cast iron and thus is heavy, transmits mechanical vibrations to the underlying concrete conduit, which vibrations frequently produce cracks in the concrete conduit and is subject to corrosion from water leakages.